1. Field of the Invention
The present invention relates to a device for highly accurately controlling an actuator such as a brushless motor that is used for a device for controlling the amount of the air intaken, for example, by an engine. More particularly, the invention relates to a device for controlling the actuator, which easily determines the unlearned state concerning the operation position of the actuator and prevents inconvenience such as erroneous control operation.
2. Prior Art
An automotive engine has, in general, been provided with various actuators that are controlled by feedback. For example, a throttle valve and a throttle actuator have been provided in the intake passage.
The throttle actuator of this type is made up of, for example, a brushless motor which, in a normal state, opens or closes the throttle valve depending upon the amount of operation of the accelerator pedal, in order to control the amount of the air intaken by the engine being interlocked to the accelerator work by a driver.
Besides, the actuator controller for electrically controlling the throttle valve is capable of controlling the throttle valve independently of the accelerator work by the driver, and can be adapted to a control device for running at a speed limit and for a traction control device.
The actuator controller (device for controlling the amount of the air intaken by the engine) of this type has been disclosed in, for example, Japanese Laid-Open Patent Publication (Kokai) No. 315641/1989. When a motor having a brush commutator is used, a hysteresis torque is produced by the rotor between the forward running and the reverse running being caused by a pushing force of the brush commutator, making it difficult to highly accurately control the position. Therefore, a brushless motor has been used.
Furthermore, Japanese Laid-Open Patent Publication (Kokai) No. 240070/1993 discloses an actuator controller in which a rotor of a brushless motor and a rotary shaft of a throttle valve are coupled together via a reduction gear in order to highly accurately control the throttle valve.
In this case, in order to change over a stator winding (hereinafter referred to as "phase") of the brushless motor, provision is made of a counter electromotive voltage detector for detecting a counter electromotive voltage generated in the phase and a current change-over detector, obviating the need of using a highly accurate and expensive revolution detector.
FIG. 5 is a diagram of constitution concretely illustrating major portions of a general actuator controller, e.g., illustrating a device for controlling a throttle actuator (brushless motor) for an automotive engine.
FIG. 6 is a plan view illustrating the constitution of magnetic poles of a motor which is the throttle actuator in FIG. 5, and illustrates a state where the throttle valve is fully closed (state where no current is supplied to the motor).
In FIGS. 5 and 6, the throttle actuator constituted by a brushless motor (hereinafter simply referred to as "actuator") 1 is constituted by a rotor 2 which is divided into four segments that are respectively magnetized in the axial direction, and a stator or a field winding 3 arranged being opposed to the rotor 2.
In FIG. 5, a rotary shaft of the rotor 2 is coupled to a rotary shaft 5a of a throttle valve 5 in an intake passage 4 communicated with an engine (not shown).
The rotary shaft 5a of the throttle valve 5 is provided with a throttle opening sensor (hereinafter simply referred to as "sensor") 6 for detecting the operation position of the throttle valve 5. The sensor 6 forms a throttle opening degree T consisting of a voltage signal to represent an operation position of the throttle valve 5.
The field winding 3 is constituted by three phase windings of a U-phase, a V-phase and a W-phase.
Furthermore, each phase is constituted by a pair of windings as represented by U1, U2, V1, V2, W1, W2 in FIG. 6.
The field winding 3 is excited by an actuator control means 7 and an actuator drive means 8 that are powered by a battery 9, and generates magnetic fluxes in the axial direction so as to be opposed to the magnetic poles of the rotor 2.
Based upon an accelerator opening degree A that represents the amount of the accelerator pedal (not shown) depressed by a driver and a throttle opening degree T fed back from the sensor 6, the actuator control means 7 which is made up of a microcomputer operates the amount (ratio for supplying a motor phase current depending upon a target throttle opening degree) for controlling the actuator 1, and outputs it as a PWM duty signal.
The actuator control means 7 receives vehicle data such as engine running speed, vehicle speed, water temperature, etc. from various sensors that are not shown. For example, the accelerator opening degree A is input as detection data from an accelerator opening degree sensor.
The actuator drive means 8 supplies a current to the field winding 3 of each of the phases depending upon the PWM duty signal from the actuator control means 7, whereby the rotor 2 is driven to open or close the throttle valve 5 thereby to control the amount of the air intaken by the engine.
The actuator drive means 8 includes a three-phase bridge circuit consisting of a group 8a of preceding-stage switching elements (power transistors), and groups 8b and 8c of final-stage switching elements (FETs), a current detector 8d for detecting a current i (see broken line) that flows into the field winding 3, and an overcurrent detector 8e.
The group 8a of preceding-stage switching elements drives the upstream side of the three-phase bridge circuit in response to the PWM duty signal, and the group 8c of switching elements drives the downstream side of the three-phase bridge circuit.
An output signal of the overcurrent detector 8e is input to the actuator control means 7 to turn off the PWM duty signal (actuator drive signal) when an overcurrent is detected to protect the device from an overcurrent.
The U-phase, V-phase and W-phase of the field winding 3 are connected between the battery and the ground via the groups 8b, 8c of final-stage switching elements.
Described below is the operation of the conventional actuator controller shown in FIGS. 5 and 6.
First, when no current is supplied to the field winding 3 of the actuator 1, the throttle valve is returned to a fully closed position by a return spring (not shown) as shown in FIG. 6. In this case, a positional relationship between the rotor 2 and the field winding 3 (stator) has been so set that a magnetic pole boundary line M1 of the rotor 2 is in agreement with a U-phase reference line M2 of the field winding 3.
When the actuator control means 7 determines a predetermined operation condition and forms a PWM duty signal corresponding to a target throttle opening degree which varies depending, for example, upon the accelerator opening degree A, the actuator drive means 8 excites the field winding 3 by flowing a current depending upon the target throttle opening degree, thereby to drive the rotor 2 and to open and close the throttle valve 5.
Thus, provision is made of a sensor for detecting the accelerator opening degree A and a sensor 6 for detecting the throttle opening degree T, the rotor 2 of the actuator 1 is coupled to the rotary shaft 5a of the throttle valve 5 supported in the intake passage 4, and the field winding 3 is excited based upon the operation data to drive the rotor 2, in order to control the amount of the air intaken by the engine.
However, the conventional device requires a current detector 8d for changing over the current-feeding phase of the actuator 1 resulting in an increase in the input I/F of the actuator control means 7. Therefore, the constitution becomes complex, bulky and drives up the cost. Moreover, when the current-feeding phase is changed over based upon the throttle opening degree T from the sensor 6, the position for changing over the current-feeding phase is deviated due to tolerance in the characteristics of the sensor 6.
In driving the brushless motor of the actuator 1, furthermore, the current suddenly changes when the current-feeding phase is changed over based upon the output of the counter electromotive voltage detector or the current change-over detector. Therefore, when the detector signal is deviated relative to a change in the magnetic flux applied to the phases, the torque produced by the actuator 1 becomes discrete and the throttle opening degree T suddenly changes.
To prevent such a sudden change, it can be contrived to employ a three-phase feeding system for feeding a current of a sinusoidal waveform to the U-, V- and W-phases independently of each other. This system, however, needs a detector for accurately measuring the rotational angle of the rotor 2, driving up the cost.
When the actuator 1, actuator control means 7 and actuator drive means 8 are combined together, furthermore, a device can be contrived in which the magnetic pole position of the rotor 2 is detected by the sensor 6 while stepwisely driving the actuator 1 according to a predetermined procedure in response to the on/off operation of a key switch (not shown), in order to store the magnetic pole positions of the rotor 2 as learned values.
In this case, the magnetic pole position of the rotor 2 is detected relying upon an output value of the sensor 6 when the actuator 1 is being normally driven and controlled at a moment when the key switch is turned on, and the learned value is found relying upon an interpolation operation, in order to control the current-feeding ratio for the phases of the field winding 3.
Even in the controller using a learned value of the operation position of the actuator 1, however, the actuator control means is not capable of determining whether the magnetic pole position of the rotor 2 has been learned or not. It is not, therefore, possible to determine whether the actuator control has been executed or not, or a trouble has been determined or not; i.e., there is a probability that the device is erroneously determined to be defective due to its own diagnosing function.
With the conventional actuator controller as described above, it is not possible to determine whether the operation positions of the actuator 1 have been learned or not even when learned values are used concerning the operation positions of the actuator 1, leaving a problem in that the device may be erroneously determined to be defective due to its own diagnosing function.